This invention relates to video signal protection and more specifically to such protection for component video.
With the advent of the Digital Video Disc (DVD) format, manufacturers and users of personal computers are incorporating the ability to playback movies or other recorded material recorded on DVD""s via the personal computer. Copy protection measures are being incorporated within these computers to protect the analog (NTSC or PAL television) video output from such a device. This is being done by incorporating bits within the digital stream on the DVD to instruct a digital to analog converter and NTSC (or PAL) encoder integrated circuit to incorporate copy protection pulses onto the analog video output signal. The copy protection techniques being used on the analog output include e.g. those in U.S. Pat. Nos. 4,631,603; 4,819,098; 4,577,216; and U.S. patent applications Ser. No. 08/784,876 filed Jan. 16, 1996; and International applications PCT/US96/17719, filed Nov. 5, 1996, and PCT/US97/05095 filed Mar. 25, 1997, all assigned to Macrovision Corporation and incorporated herein by reference.
A computer display uses a VGA (or similar or equivalent) output signal of the computer. This VGA output signal (xe2x80x9ccomponent videoxe2x80x9d) is provided on a multiwire bus that provides separately a red video signal, a green video signal, a blue video signal, a set of vertical synchronizing pulses and a set of horizontal synchronizing pulses. The frame rate (refresh rate) is usually 60 frames per second. VGA does not require any one format (resolution) in terms of pixels per line or lines per frame or refresh rate; a variety of pixels per line and lines per frame are accommodated within the VGA standard.
There has been a growing after market for VGA to NTSC (or PAL) converters that take the VGA signal described above and convert it into an NTSC or PAL (composite) video signal for display on a regular TV monitor, TV set or video projector. With such a converter device connected to receive a VGA output signal, a user converts the VGA output signal to an NTSC or PAL output signal and then can record the NTSC/PAL output signal using a conventional VCR (video cassette recorder), thus circumventing the analog copy protection described above. While the video quality of such a conversion may be inferior, that may not deter a determined pirate.
Therefore there is a need for protection of a VGA video signal that meets the usual requirements for an effective video protection system. A useful video protection system meets two basic requirements. First any copy made must result in an inferior quality picture. This is called effectiveness. In this case, a user who connects a video cassette recorder to a VGA to NTSC (PAL) converter must get a signal therefrom of inferior entertainment quality. Tearing of the picture, amplitude variation or loss of color are examples of inferior entertainment quality. The counterbalancing requirement is that the VGA signal when viewed on a VGA monitor must be totally xe2x80x9cplayablexe2x80x9d, e.g. not display any artifacts in the picture. The present protection technique balances these two requirements.
The present VGA protection method modifies at least one of the synchronization (xe2x80x9csyncxe2x80x9d) pulse trains that are part of the VGA video signal. These modifications include deletion and/or addition of certain sync pulses, changing of the duty cycle of certain pulses, and switching between one or more of the above methods on a fixed, psuedo-random or random basis on various frames of the video signal. The additions and/or deletions can be in the vertical blanking intervals or the horizontal blanking intervals of the VGA video signal.
Thus in accordance with this invention, VGA video signals are protected from copying (or even from viewing) after being subject to NTSC/PAL conversion by modifying at least one of the horizontal and/or synchronization pulse trains that are part of the VGA video signal. In this context xe2x80x9cVGAxe2x80x9d refers to the well known Video Graphics Array video standard commonly used in the computer field and also to the associated SVGA and IBM""s XVGA standards, which for purpose of this invention are the same.
Moreover, while one embodiment is directed to VGA signals provided from a DVD player installed in a computer, clearly the invention is not so limited and generally applies to VGA video signals whether output from a DVD player installed in a computer, other types of digital video players, or to any type of component computer video output. Of course, it is to be understood that a typical application is to copy protect copyrighted material, which is typically movies provided on DVD, but the invention is not so limited.
Hence in accordance with the invention, in one embodiment the horizontal sync pulses in the vertical blanking interval of a VGA signal are modified. The resulting modified VGA signal is readily viewable on any VGA monitor. However, if this signal is converted to an NTSC/PAL signal by one of the well known commercially available VGA to NTSC/PAL converters, the resulting signal is relatively unviewable on a NTSC/PAL television or television monitor. Also, if an attempt is made to copy this signal for instance using a conventional NTSC/PAL VCR (video cassette recorder), the resulting recording is also unviewable. By unviewable is meant a picture exhibiting artifacts, as described above, which substantially degrade the resulting picture when displayed on the television set.
It has been found that the most advantageous modifications to the sync pulses in accordance with this invention are to modify the horizontal sync pulse in the first part of the vertical blanking interval, e.g. prior to the occurrence of the vertical sync pulse. This typically means in the first 10 lines of the vertical blanking interval (VBI). Also, it has been found that in general it is undesirable to have a net increase in the total number of horizontal sync pulses in the VBI in any one video frame since this tends to adversely affect some VGA monitors.
Hence in one embodiment, one or more horizontal sync pulses are deleted from the first part of the vertical blanking interval. For increased effectiveness of the copy protection, one horizontal sync pulse is added, but in a place where such a horizontal sync pulse is not normally present, e.g. in the middle of a particular horizontal video line. The pattern by which horizontal sync pulses are deleted and/or added may be the same in every frame, or may vary from frame-to-frame. If it varies, the variation may be a fixed pattern, a pseudo-randomly varying pattern, or a randomly varying pattern. The varying patterns have been found to increase copy protection effectiveness. In another embodiment, the number of horizontal sync pulses is increased by adding several horizontal sync pulses to each line, for instance in the first portion of the vertical blanking interval. As mentioned above, with some VGA monitors, this degrades playability.
Other patterns for removal and/or addition of horizontal sync pulses are also possible.
Also in accordance with other embodiment, the vertical sync signal is altered, but this has been found to affect some VGA monitors adversely.
Also in accordance with the invention, a particular modification pattern to the sync pulses is dependent upon the characteristics of the attached VGA monitor. This is possible because in the computer environment, it is possible for the computer to xe2x80x9cknowxe2x80x9d the characteristics of the attached VGA monitor as supplied by the user. In this case, the particular modification pattern may be set adaptively to accommodate the particular VGA monitor so as to minimize adverse affects on playability. Also, the present VGA copy protection scheme may be turned on or off either by content present in the source video material, e.g. on the DVD, or otherwise. This turning on and off may be either only to protect certain (copyrighted) material or may be done to increase the effectiveness of the anti-copy protection scheme by periodically switching between different versions of the process and/or by turning it on and off, thus further confusing any VGA to NTSC/PAL converter.
It should be noted that while some VGA to NTSC converters will produce a static response to a particular version of the present protection signal, a majority of converters exhibit picture tear dynamically or produce non-copiable results.
This static response to the protection signal may be in the form of a static picture shift and or static brightness change and/or static distortion (i.e. tear) in the picture when the output of the converter is connected to the TV set or VCR. However, this static response would be still copiable and viewable on a VCR and TV set. Therefore, to increase the annoyance factor, the particular protection signal may be turned off for a short time in a periodic or random fashion. By turning off the protection from time to time, the output of converter will have a dynamically shifted picture and/or dynamically distorted picture when connected to a TV set and/or VCR. This causes a more effective protection signal when the converter is connected to a VCR (and also a less viewable picture on the TV set).
Of course, it may be even more effective to affect a greater population of converters by alternating different protection processes in accordance with the invention along with turning off the protection from time to time.
While the references here to television typically are in terms of NTSC/PAL, other television standards, e.g. SECAM would also be vulnerable to the present modifications.
Also, circuitry is disclosed herein for suitably modifying the VGA video signal so that it contains the protection modifications. While several such embodiments are disclosed, it is to be understood that these are not limiting and a wide variety of other circuits would provide the desired modifications. Moreover, the circuits described herein only provide certain types of modifications, whereas a greater range of modifications in disclosed herein. It would be well within the skill of one of ordinary skill in the art to design and build circuitry to carry out the other types of modifications disclosed herein.
For example, the horizontal sync pulse modifications need not be restricted to the vertical blanking interval. Horizontal sync pulse train deletions and/or additions can be in the vicinity of the vertical blanking interval or anywhere in the field including in the active field. In some cases the horizontal sync pulse train is modified anywhere in the field by horizontal sync pulse splitting, pulse width modulation and the like. Also, vertical sync pulse train modifications can be made by adding pulses in the vertical sync pulse train. Other vertical sync pulse train modifications may include vertical sync pulse width modulation and/or splitting.
Because it is possible for the computer to be informed (or set by the user) as to which monitor is connected thereto, maximum copy protection effectiveness for VGA type converter boxes can be achieved with yet an additional copy protection signal. For instance, in certain monitors, the video clamp pulse may be coincident to the first 70% of the horizontal blanking interval of the red, green and blue video channels. Therefore, an additional copy protection method modifies the video channels with peak white pulses during the last 30% of the horizontal blanking interval.
Therefore in some cases an anticopy signal is inserted into at least a portion of the horizontal blanking interval (or in the vicinity of the horizontal blanking interval) over a sufficient number of lines of the component video signal (i.e. any combination of red, green, and/or blue). This anticopy signal may be an xe2x80x9cAGCxe2x80x9d pulse as described in U.S. Pat. No. 4,631,603, referred to above. Also, this anticopy signal can be a static and/or periodic and/or random and/or pseudo-random signal of various amplitudes and/or frequencies and/or phases and/or positions and/or widths.
Also, while the particular illustrated circuitry for providing these modifications is shown as isolated circuits, these circuits may be incorporated for instance on an integrated circuit which includes other functionality and which is installed in the computer which hosts the DVD player, or otherwise connected thereto. It is to be expected that in one commercial embodiment, the present circuitry is included in an integrated circuit associated with the DVD player and which performs other functions for controlling the DVD player and/or its output.
Additionally, a method of defeating such a protection scheme is disclosed herein, to protect the users of the protection (e.g. copyright owners) from unlicensed individuals that make, use and sell so called xe2x80x9cdefeatxe2x80x9d devices. A similar pattern of copy protection technologies and corresponding defeat devices are known in the analog video copy protection technologies referred to above.
Therefore an associated protection defeat method and apparatus includes inputting the modified synchronizing pulses to a synchronizing generator that uses one or more of the modified pulse trains to generate a proper horizontal and vertical synchronizing pulse train. This proper pulse train when connected to a VGA to NTSC/PAL converter produces copiable NTSC/PAL video signals.